Don't bother poisoning lists; it costs code size.

src/include/gpxe/list.h

-#ifndef _LIST_H
-#define _LIST_H
+#ifndef _GPXE_LIST_H
+#define _GPXE_LIST_H
 
 /** @file
  *
 
 #include <stddef.h>
 
-/*
- * These are non-NULL pointers that will result in page faults
- * under normal circumstances, used to verify that nobody uses
- * non-initialized list entries.
- */
-#define LIST_POISON1 ( ( void * ) 0x00100100 )
-#define LIST_POISON2 ( ( void * ) 0x00200200 )
-
 /*
  * Simple doubly linked list implementation.
  *
  */
 static inline void list_del ( struct list_head *entry ) {
 	__list_del ( entry->prev, entry->next );
-	entry->next = LIST_POISON1;
-	entry->prev = LIST_POISON2;
 }
 
 /**
 	      &pos->member != (head);					      \
 	      pos = list_entry ( pos->member.next, typeof ( *pos ), member ) )
 
-#endif /* _LIST_H */
+#endif /* _GPXE_LIST_H */